Tailless connector



Oct. 31, 1967 E. J. SCHAUMANN TA ILLES S CONNECTOR Filed July 15, .1966

INVENTOR ERIK u. SCHAUMANN ATTORNEY United States Patent Oflice3,349,706 TAILLESS CONNECTOR Erik J. Schaumann, Oakland, N.J., assignorto E. I. du Pont de Nemours and Company, Wilmington, Del., a corporationof Delaware Filed July 15, 1966, Ser. No. 565,502 5 Claims. (Cl. 102-27)This invention relates to the art of blasting with explosives andparticularly to a connector for securely positioning detonating fuse anda delay device in operative relationship so that a detonation stimuluscan be propagated from one to the other.

, Commercial blasting operations often employ detonating fuse or cord inconjunction with delay devices whose function is to permit firing themain blasting charges in the desired sequence. In such assemblies, it isnecessary to secure the explosive cord in propagating relationship tothe delay device so that the detonation impulse from one will bereliably propagated to the other. Typical of the means used heretoforefor this purpose is the delay connector described in US. 2,736,263. Thisconnector comprises a tubular metal shell which centrally houses anencapsulated delay train, the ends of which abut the cut ends of lengths(tails) of detonating fuse, e.g., Primacord, that are crimped into theshells initially open ends. In the field, the connector is inserted intothe blasting array by cutting a trunk line of detonating fuse andsecuring the tails of Prirnacord to. the two cut ends with a square knotor tape. Although these connectors are superior to other available typesof connectors, provision of the tails of detonating fuse both increasesthe cost of manufacturing the connectors and complicates theirclassification and shipment. Also, in spite of the skill and careexercised by the blasting technician, moisture can seep through thecrimped joint between the detonating fuse and metal shell and then intothe cut end of each tail of detonating fuse, thus desensitizing itsexplosive core.

Accordingly, this invention provides an inexpensive, reliable and easilymanipulated, tailless connector for securing detonating fuse to each endof a delay device or unit in the field without using special tools. Theconnector comprises a central tubular portion whose bore is adapted toreceive the tubular shell of a delay unit; a fuse-receiving section ateach end of the tubular portion and communicating with its bore, eachsuch section being adapted to internally receive a substantially U-shaped segment of detonating fuse with the two arms of the U lying insubstantially the same plane as the longitudinal axis of the bore andthe apex of the U positioned adjacent the end of the bore, and having apair of oppositely disposed apertures whose axis is substantiallyperpendicular to said plane; and

two tapered pins, one mateable with each pair of apertures and adaptedto extend through the apertures and between the arms of the U-shapedsegment of fuse, and to hold the apex of the U adjacent the end of thedelay unit.

Preferably the tailless connector of this invention is of one-piececonstruction with the tapered pins integrally connected to the centraltubular portion or the fuse-receiving sections by thin flexible webs.Such a connector is conveniently made of thermoplastic by injectionmolding.

By detonating fuse is meant relatively brisant detonation-transmittingexplosive cords that will both accept and donate a detonation stimulusthrough their sides. Such cords include the conventional Primacord,E-Cord, and Detacord detonating fuses which contain a core of highvelocity detonating explosive, usually PETN, encased in a flexibletextile sheath, and the more recently devel- 3,349,796 Patented Oct. 31,1967 oped flexible extruded explosive cords such as the commerciallyavailable Detaflex cords described in US. 2,992,087 or US. 2,999,743,and the cord described in coassigned, copending application S.N.481,150, filed Aug. 19, 1965, which comprises superfine high explosivesuch as PETN in a plasticized polymeric metallocarboxylate elastomerbinder, preferably containing a central reinforcing element (string) anda polyurethane.

The terms delay unit and delay device refer to devices comprising atubular shell that encapsulates a oneor two-way delay train which may beof the type known in the art, e.g., as described in US. 2,475,875 or US.2,736,263.

In order to describe this invention in greater detail, reference is nowmade to the accompanying drawings wherein:

FIGURE 1 is a side view, in partial section, of a preferred connector ofthis invention, showing a length of detonating fuse in one end inpropagating relationship to a delay unit,

FIGURE 2 is an end view of the same connector, and

FIGURE 3 is a partially sectional plan view of the connector of FIGURE1.

In the drawings, which show the relative sizes of the various componentsof the connector, like numerical designations designate like parts.

Referring now to the drawings, there is shown a onepiece body ofthermoplastic material having a central tubular portion 1 with an axialbore 1a which communicates at each of its ends with identicalfuse-receiving sections 2, whose configuration is generally that of asemielliptic arch (semielliptic paraboloid) having a major axis a(FIGURE 3) that is coaxial with the longitudinal axis of bore 1a, aminor axis b, and a height h (FIGURE 2). A pair of oppositely disposedapertures 3 extend transversely through each semielliptic arch section2, with the axis of each pair being normal to the longitudinal axis ofbore 1a. Tapered pins 4, one of which is shown in its operating positionin FIGURE 1 and the other of which is shown in its as-molded position inFIGURE 3, have vertical ribs 4a of triangular cross-section, thattightly engage the periphery of the apertures. Each pin 4 is integrallyconnected by a thin flexible web 5 to the side of the fuse-receivingsection 2 with which it is to cooperate. This positioning of the webspermits inserting pin 4 into apertures 3 from either the top or bottomof the connector, positioned as shown in FIGURE 1.

From FIGURES 1 and 3, it is seen that apertures 3 are positionedrelative to the end of bore 1a and the position of the U-shaped segmentof detonating fuse 6 so that the tapered pins pass between arms 6a ofthe fuse and wedge its apex 6b against the end of delay device 7. Forproper staking action by pins 4, the space between arms 6a preferably isat least about equal to the fuses diameter, and accordingly, axis b ofsection 2 is at least about three times the fuses diameter. Contactbetween apex 6b and the end of delay 7 is preferred, but not essentialwhere the air-gap sensitivity of the detonating fuse or base charge ofthe delay unit, as the case may be, is such that detonation will bepropagated from one to the other absent such contact. For example, 50grain per foot Primacord will propagate a detonation impulse through itssheath and over a gap of about 4 inch and will be initiated through itssheath by a delay unit containing a base charge of 4.8 grains of leadazide spaced from the apex of the fuse by up to /1 inch.

As best seen in FIGURE 2, each fuse-receiving section 2 has a pair ofoppositely disposed arcuate passages 8 of slightly larger diameter thanbore 1a, thereby facilitating insertion of the delay device into thebore. These passages are optional and would not be needed where theheight J) h of sections 2 is larger than the diameter of bore 1a. Thediameter of bore 1a is such that it peripherally engages delay device 7,a snug force fit being preferred.

Although the particular construction of the delay device does notconstitute part of this invention, I prefer to use a symmetrical two-waydelay device having a delay train of the type described in U.S.2,736,263, e.g., one composed of a central thick-walled lead tube havingan axial bore, and in sequence from each end of the bore, (1) anexothermic charge such as, e.g., a 30/35/35 mixture, by weight ofmagnesium, barium peroxide and selenium, (2) a thin metal partition, (3)a heat-sensitive charge such as an 85/ 15 lead azide/t-etracene mixture,by weight, and (4) a terminal base charge of detonating explosive, e.g.,lead azide. This delay train is encapsulated by inverting a metalcapsule over each end of the train, inserting this assembly in a metalsleeve of about the same length, and then crimping the sleeve andcapsules in place around the lead tube, thus completing construction ofthe delay unit. Delay units of the type described in coassigned,copending application S.N. 517,317, filed Dec. 29, 1965, can also beemployed.

The delay unit prefer-ably is inserted in, and thus made part of theconnector before it is sent to the field so that the user only needinsert segments of detonating fuse in each of the fuse-receivingsections. This is done simply by folding back about two or more inchesof the fuse at its cut end to form a U-shaped loop and then insertingthis loop into the fuse-receiving section of the connector until theapex of the U abuts the end of the delay unit. After the U-loopedsection of fuse is thus inserted, pin 4 is inserted through the alignedapertures 3 passing between the arms of fuse, providing a compressiveand staking action which helps retain the configuration of the U-loopand maintains the apex of the loop in propagating relationship to thedelay unit.

The connector can be made of any suitable thermoplastic material, suchas polypropylene, acetal resins, polytetrafluoroethylene, nylon,unplasticized polyvinyl chloride, polystyrene, acrylic polymers,polyurethanes, and phenolic resins having the appropriatecharacteristics of strength, tear resistance, and flexibility. Thematerial chosen should not be subject to undue hardening in coldtemperatures or undue softening at warm temperatures. The high densitypolyethylene resin, commercially available as Alathon 7516, isparticularly satisfactory for manufacturing the connectors by injectionmolding.

An embodiment of the invention preferred for use with detonating fuseshaving an outside diameter between about 0.14 and 0.24 inch, e.g., 50grain/foot Primacord and 25 grain/ foot E-Cord, and a delay unit about1.75 inches long and 0.25 inch in diameter, is made of Alathon 7516 inthe configuration shown in FIGURES 1 to 3 and has an overall length ofabout 4 inches; a wall thickness of about 00.5 to 0.08 inch; a bore 1aof about the same diameter and length as the delay element;fuse-receiving sections 2 having a major axis a of about 1.13 inch, aminor axis [1 of about 0.7 inch, a height h of about 0.25 inch, arcuatepassages 8 having a diameter of about 0.27 inch, and about 0.3inch-diameter apertures 3 whose centers are about 0.86 inch from theends of the connector; and tapered pins 4 about 1.4 inches long, whichhave a maximum diameter (including the ribs) about 0.03 inch larger thanthe diameter of apertures 3 and are integrally connected to the sides ofthe fuse-receiving sections by webs 5 having a diameter of about from0.06 to 0.08 inch and an overall length of about 2.75 to 3.00 inches.

I claim:

1. A tailless connector for holding detonating fuse in propagatingrelationship to each end of a delay unit, comprising a central tubularportion whose bore is adapted to receive the tubular shell of a delayunit; a fuse-receiving section at each end of the tubular portion andcommunicatin g with its bore, each such section being adapted tointernally receive a substantially U- shaped segment of detonating fusewith the two arms of the U lying in substantially the .same plane as thelongtiudinal axis of the bore and the apex of the U positioned adjacentthe end of the bore, and having a pair of oppositely disposed apertureswhose axis is substantially perpendicular to said plane; and two taperedpins, one mateable with each pair of apertures and adapted to extendthrough the apertures and between the arms of the U-shaped segment offuse, and to hold the apex of the U adjacent the end of the delay unit.

2. A connector of claim 1 which is of one-piece, thermoplasticconstruction and wherein each tapered pin is attached to thefuse-receiving section with which it cooperates by a thin flexible webof the thermoplastic.

3. A connector of claim 2 wherein the pins are substantially verticallyribbed.

4. A connector of claim 2 wherein a tubular delay unit of substantiallythe same length as the bore in the tubular portion is peripherallyengaged by the walls of said bore.

5. A connector of claim 2 wherein the tubular portion is of cylindricalconfiguration and each fuse-receiving section is of semielliptic archconfiguration.

References Cited UNITED STATES PATENTS 2,736,263 2/1956 Lewis et a1l0227 X 2,952,206 9/ 1960 Becksted l0227 3,020,844 2/ 1962 Miller l02273,175,491 3/ 1965 Robertson 102-27 FOREIGN PATENTS 707,129 4/1965Canada.

BENJAMIN A. BORCHELT, Primary Examiner.

V. R. PENDEGRASS, Assistant Examiner.

1. A TAILLESS CONNECTOR FOR HOLDING DETONATING FUSE IN PROPAGATINGRELATIONSHIP TO EACH END OF A DELAY UNIT, COMPRISING A CENTRAL TUBULARPORTION WHOSE BORE IS ADAPTED TO RECEIVE THE TUBULAR SHEET OF A DELAYUNIT; A FUSE-RECEIVING SECTION AT EACH END OF THE TUBULAR PORTION ANDCOMMUNICATING WITH ITS BORE, EACH SUCH SECTION BEING ADAPTED SEGMENT OFDETONATING FUSE WITH THE TWO ARMS SHAPED SEGMENT OF DETONATING FUSE WITHTHE TWO ARMS OF THE U LYING IN SUBSTANTIALLY THE SAME PLANE AS THELONGITUDINAL AXIS OF THE BORE AND THE APEX OF THE U POSITIONED ADJACENTTHE END OF THE BORE, AND HAVING A PAIR OF OPPOSITELY DISPOSED APERTURESWHOSE AXIS IS SUBSTANTIALLY PERPENDICULAR TO SAID PLANE; AND TWO TAPEREDPINS, ONE MATEABLE WITH EACH PAIR OF APERTURES AND ADPATED TO EXTENDTHROUGH THE APERTURES AND BETWEEN THE ARMS OF THE U-SHAPED SEGMENT OFFUSE, AND TO HOLD THE APEX OF THE U ADJACENT THE END OF THE DELAY UNIT.